This invention relates to a declutchable manual override gearbox, in particular such a gearbox for use with rotary actuators, for example pneumatic rotary actuators.
Rotary actuators are used in a great variety of applications. There are many designs of rotary actuator, including examples actuated by hydraulic pressure, pneumatic pressure and electric drives. It is also known to use position controllers to modulate the position of the actuator. All of these various designs have in common the purpose of providing an output torque which can be utilised to drive another device or mechanism.
By way of example, one common application for bi-directional rotary actuators is the positioning of large damper valves controlling the flow of air and other gases along ducting in power generating plants. These dampers are often inaccessible, so it is not possible to install drives immediately adjacent the valve. In such circumstances, the rotary actuator drives the damper valve via a mechanical linkage. The rotary actuator will, in most cases, be used in conjunction with a position controller to provide for accurate control of the position of the damper valve.
In this, and other applications of rotary actuators, it can sometimes be desirable to provide for manual adjustment of the position of the actuator, for example during the initial set-up of a mechanism, or on failure of automatic actuator function. This is generally accomplished by using a so called declutchable manual override gearbox. The gearbox is mounted adjacent to the actuator and is connected to the output of the actuator. Drive is transferred via the gearbox to a drive shaft connected to the gearbox output. The gearbox includes a manually operable override, typically a wheel or lever, selectively engageable with the drive train in the gearbox. In normal operation, this manual override is de-clutched from the drive train. However, if it is desired to manually adjust the position of the actuator and the mechanism it drives, the manual override can be engaged.
FIG. 1 illustrates a prior art drive for a damper valve. The damper valve (not shown) is driven through a push rod (also not shown), which is in turn driven by a lever 102. The lever is mounted on the end of a heavy duty drive shaft 104, the otherend of this drive shaft being drivably connected to the output of a declutchable manual override gearbox 106. The drive shaft 104 is driven via the gearbox by a bidirectional pneumatic rotary actuator 108, the position of which between end limiting positions is modulated by a position controller 110. The drive shaft 104 is supported at its end adjacent to the lever 102 by a support bearing 112 mounted on a carrier bracket 114. The carrier bracket is itself supported on a floor mounted stand 116, to which it is welded. The carrier bracket 114 is also provided with mounting points to which the gearbox 106 is mounted to be suspended cantilever-like from the carrier bracket 114. The weight of the pneumatic actuator and its position controller is also borne by the gearbox mounting points of the side of the carrier bracket 114.
Conveniently, such an arrangement can be assembled by selecting and fitting together a standard, xe2x80x9coff-the-shelfxe2x80x9d actuator, position controller and gearbox. However, it is necessary to use a custom-made carrier bracket and floor mounted stand. The drive shaft also has to be custom-made and an appropriate support bearing selected and mounted on the carrier bracket. Often these custom made parts are unique to one particular installation and consequently contribute a substantial proportion of the total cost of the equipment.
It is an object of the present invention to provide a declutchable manual override gearbox, preferably suitable for use with a rotary actuator (although not necessarily exclusively for such use), for example a pneumatic rotary actuator, which facilitates a more compact drive arrangement through which the actuator can drive other devices or mechanisms.
It is another object of the present invention to provide such a gearbox that minimises the need for custom-made parts in the drive arrangement.
In one aspect, the present invention provides a declutchable manual override gearbox, comprising a casing, and a drive shaft mounted for rotation within the casing. The drive shaft has an input end and an output end, the input end of the drive shaft adapted to engage the output of a rotary actuator (or other drive means) and the output end of the drive shaft adapted for attachment to an element to be driven by the actuator or gearbox. Manual override means are provided for manually rotating the drive shaft, the gearbox also including means for selectively rendering the manual override means inoperative. Means associated with a base portion of the casing enable mounting of the gearbox on an underlying support stand.
In another aspect, the invention provides a drive arrangement for a device or mechanism, comprising a rotary actuator, a declutchable manual override gearbox as defined above, and a support stand below the gearbox on which the gearbox is supported.
The above and other objects will be exemplified in the following description of specific embodiments of the invention.